This invention relates generally to the art of orthopaedic prostheses, and more particularly to the type of prosthesis which is adapted to promote the ingrowth of bone and/or tissue into the portion of the prosthesis surface in contact with the bone surface. Therefore, this type of prosthesis is generally not used with any bone cement or grouting material.
It is known in the art to adapt the portion of the prosthesis surface in contact with the bone to promote bone growth.
U.S. Pat. No. 3,855,638 (Robert M. Pilliar) describes a prosthetic device comprised of a solid metallic material substrate and a porous coating of metallic material adhered to and extending over a portion of the substrate surface. The porous coating described in this Pilliar patent consists of a plurality of small ball-shaped metallic particles which are bonded together at their points of contact with each other and said substrate to define a plurality of connected, interstitial pores uniformly distributed throughout the coating. This particular coating is described more fully in the Pilliar patent. It is an example of a type of porous coating which is adaptable or suitable for ingrowth of boney tissue into the porous coating.
U.S. Pat. No. 3,906,550 (Rostoker, et al) describes a prosthetic device which includes a porous fiber metal structure formed from the strands substantially sinusoidally shaped fiber strands. The points of contact between the fibers become metallurgically bonded by a sintering process. The particular fiber metal structure is described more fully in the Rostoker et al patent. This fiber metal structure provides at least a portion of the surface of the prosthetic device which is to be adjacent to the skeletal structure to enable bone and soft tissue growth into the fiber metal structure. Lines 35-44 in Column 3 of the Rostoker et al patent indicated a number of ways for securing the metal fiber structure to a solid metal portion. The preferred means is to metallurgically bond the fibers contacting the surface of a solid metal portion. Line 60 of Column 3 indicates that, in one particular embodiment of the invention, a wear insert is molded integrally with the fiber structure portion. The specification further indicates in lines 61-64 that the insert (which is not subject to bone ingrowth) can be held in place mechanically so that the insert can be subsequently removed and replaced if necessary. This statement seems to indicate that the wear insert is not actually molded to the fiber structure, by instead that the fiber structure is molded into shape about the already formed insert. The specification does not indicate what type of material the wear insert is. It is assumed that it could be any appropriate wear material appropriate for use in the body.
U.K. Patent No. 1,554,454 (Jack Chester Bokros) describes an implantable prosthetic device having a region of controlled porosity to promote the ingrowth of bone and/or tissue. This region is formed by a metal coil spring having a plurality of spaced apart points secured to the other points of the spring or substrate. It is indicated on page 2 of the specification, in lines 64 to 68, that the coil springs are preferably made from the same metal as the remainder of the prosthesis, however, in some cases, dissimilar metals are sometimes employed. Therefore, it appears that the metal coil spring portion of Bokros is intended for use with a metal substrate. It is indicated that the device is sintered in order for the portion of the spring in contact with the metal substrate to be bonded to the substrate, as well as for the touching loops of the helical springs to be sintered to one another at the points of contact.
It is also known in the art of prosthetic devices to reinforce non-metallic components (such as a polyethylene tibial knee component) by utilizing various types of metal retainers. This type of combination allows the non-metallic portion to be utilized as a bearing surface while the retainer is used for structural purposes. When any load is applied to the bearing surface, it is transmitted through the plastic to the metal retainer which distributes the load more evenly over the entire prosthesis. An example of one type of metal retainer is described in Jean-Marie Cloutier's U.S. Pat. No. 4,207,627.